Vehicle-mounted air compressors are used to unload dry and liquid bulk goods from large pressurized vessels and container trucks and trailers. The technique involves pumping compressed air into the top end of a vessel/container while opening a valve in a lower end of the vessel/container to allow the dry or liquid goods to be conveyed out of the mobile vessel/container and into a different storage unit. Examples of dry products conveyed out of vehicles using this technique include flour, wheat, cereal, cornstarch, synthetic powder, granulated products, cement, limestone, and fly ash. Examples of liquid products conveyed out of vehicles using this technique include chemicals, solvents, food, liquid sugar, molasses, and bitumen.
When a compressor is mounted on a vehicle, the compressor is commonly driven off of the engine that drives the vehicle. As a result, the speed of the compressor is typically proportional to the speed at which the vehicle's engine drives a compressor. The vehicle engine speed can vary depending on the size and type of engine, and on the vehicle and environment in which the compressor is used.
Noise from the compressor is a concern to vehicle operators because of the existing health and safety regulations, and especially in situations where the vehicles are used to unload dry and liquid goods in densely-populated areas. Specifically, pressure pulsations generated at the discharge and/or suction port of a compressor is a major contributor to the total noise of the compressor. Pressure pulsations propagate through the entire piping system and radiate through the walls of the pipes. Silencers are commonly used to reduce the severity of these pressure pulsations.